This research study examines the effects of exercise on carbohydrate metabolism and estrogen levels in postmenopausal women receiving two routes of administration of estrogen replacement therapy (ERT). ERT is the administration of the female sex hormone, estrogen, after women have reached menopause. The research will involve the use of commonly used,, approved hormonal medications. These treatments will be used to aid in the investigation: however, the purpose of the study is not to test the estrogen replacement medications.